Synthetic polymeric compositions which are bioerodible and biocompatible have become increasingly important and valuable in recent years. One application for such compositions is as surgically implantable biomaterials or prosthetic articles for human and animal subjects in-vivo. Consequently, such biomaterials are articles which serve as implants, a tangible item to be inserted into a living site as for growth or formation of an organic union, or prostheses, artificial devices introduced into living tissues to replace a missing part of the body; these are exemplified by articles such as vascular grafts, biodegradable sutures and pellets, and orthopedic appliances such as bone plates and the like. In order for an implantable or prosthetic article to be truly useful, it should be composed of a synthetic polymeric composition having specific characteristics and properties: First, the polymeric composition should have a surface that permits and encourages growth of appropriate mammalian cell types; that is, the growing and maintenance of cells on, and if appropriate, within, its matrix, after introduction into a subject in-vivo. For the purposes of graft materials, one objective is to maintain non-thrombogenic surfaces similar to that as exists in living tissues. A failure to initiate and maintain such endothelial cell surface layers leads to the occurrence of thrombotic events such as occlusion of the blood vessel(s) an ultimate failure of the implanted or prosthetic article. Second, the synthetic composition should provide sufficient elasticity and tensile strength over a preselected minimal time period which will vary with the specific application. Third, the synthetic composition should be non-immunogenic, biocompatible, biodegradable in-vivo and yield degradation products which are themselves non-inflammatory, non-toxic, and non-antigenic. Lastly, the ideal material should degrade within predictable periods of time and be suitable for introduction at multiple tissue sites thereby eliminating the need for surgical removal.
Despite continuing research efforts, no class of synthetic polymeric biomaterials has yet been developed which provides all these desired attributes. For example, most of the research concerning synthetic grafting materials has utilized compositions such as Dacron [Graham et al., Arch. Surg. 115:929-933 (1980); Herring et al., Ann. Surg. 190:84-90 (1979)]. These materials, however, never develop the desired endothelial cell intima necessary to maintain a non-thrombogenic surface; as a result, thrombosis--blood vessel blockage and diminished blood cell supply to organs in the body--often occurs. Similarly, the use of polygalactin mesh has failed to provide the necessary surface erosion characteristics and thus is unpredictable in degradation time [Bowald et al., Surgery 86:722-729 (1979)]. Other presently known biodegradable polymers such as polylactic acid, polyglycolic acid, polycaproloctones and the various polyamides also all degrade irregularly and unpredictably with a demonstratable loss of permeability and mechanical strength over time [Heller et al., "Theory and Practice of Control Drug Delivery from Bioerodible Polymers", in Controlled Release Of Bioactive Material, R. W. Baker Editors, Academic Press, New York, 1980, pp. 1-17; Pitt et al., Biomaterials 2:215-220 (1981); Chu, C. C., J. Appl. Polym. Sci. 26:1727-1734 (1981)]. Insofar as is presently known, therefore, no synthetic polymeric composition offers all the properties and characteristics which would make it desirable for use as an article for prosthesis or implantation in-vivo.